UefiCpuPkg/MpLib: add support to register GHCB GPA when SEV-SNP is enabled

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

An SEV-SNP guest requires that the physical address of the GHCB must
be registered with the hypervisor before using it. See the GHCB
specification section 2.3.2 for more details.

Cc: Michael Roth <michael.roth@amd.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Ray Ni <ray.ni@Intel.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm

@@ -15,6 +15,57 @@
 
 %define SIZE_4KB    0x1000
 
+RegisterGhcbGpa:
+    ;
+    ; Register GHCB GPA when SEV-SNP is enabled
+    ;
+    lea        edi, [esi + MP_CPU_EXCHANGE_INFO_FIELD (SevSnpIsEnabled)]
+    cmp        byte [edi], 1        ; SevSnpIsEnabled
+    jne        RegisterGhcbGpaDone
+
+    ; Save the rdi and rsi to used for later comparison
+    push       rdi
+    push       rsi
+    mov        edi, eax
+    mov        esi, edx
+    or         eax, 18              ; Ghcb registration request
+    wrmsr
+    rep vmmcall
+    rdmsr
+    mov        r12, rax
+    and        r12, 0fffh
+    cmp        r12, 19              ; Ghcb registration response
+    jne        GhcbGpaRegisterFailure
+
+    ; Verify that GPA is not changed
+    and        eax, 0fffff000h
+    cmp        edi, eax
+    jne        GhcbGpaRegisterFailure
+    cmp        esi, edx
+    jne        GhcbGpaRegisterFailure
+    pop        rsi
+    pop        rdi
+    jmp        RegisterGhcbGpaDone
+
+    ;
+    ; Request the guest termination
+    ;
+GhcbGpaRegisterFailure:
+    xor        edx, edx
+    mov        eax, 256             ; GHCB terminate
+    wrmsr
+    rep vmmcall
+
+    ; We should not return from the above terminate request, but if we do
+    ; then enter into the hlt loop.
+DoHltLoop:
+    cli
+    hlt
+    jmp        DoHltLoop
+
+RegisterGhcbGpaDone:
+    OneTimeCallRet    RegisterGhcbGpa
+
 ;
 ; The function checks whether SEV-ES is enabled, if enabled
 ; then setup the GHCB page.
@@ -39,6 +90,9 @@ SevEsSetupGhcb:
     mov        rdx, rax
     shr        rdx, 32
     mov        rcx, 0xc0010130
+
+    OneTimeCall RegisterGhcbGpa
+
     wrmsr
 
 SevEsSetupGhcbExit: